main.c: 
int main (void) {
int a, b;
printf("enter two numbers:");
scanf("%d %d", &a, &b);
printf("add:%d\n",
sub (a, b));
printf("sub:%d\n", 
sub (a, b));
printf ("mul :%d\n", 
mul (a, b));
printf("div :%lf\n", 
div (a, b));
return 0;

}